1. Field of the Invention
The present invention relates to a valve for controlling fluids for a reservoir injection system, such as a Diesel or gasoline injection valve.
2. Description of the Prior Art
Various versions of fuel injection valves are known. Most recently, such fuel injection valves have been actuated by a piezoelectric actuator, which controls a motion of a nozzle needle for injecting fuel. With such piezoelectric actuators, very short switching times can be achieved in particular. However, the piezoelectric actuators have the disadvantage that they have changes in length upon changes in temperature, such as an increase in temperature in the engine compartment while an engine is in operation. Moreover, the stroke of the piezoelectric actuators is relatively short. So-called hydraulic boosters are therefore used to boost the stroke of the piezoelectric actuator. The hydraulic boosters simultaneously have the advantage of being capable of compensating for temperature-caused changes in length of the piezoelectric actuator, by reducing the volume in the booster chamber. Typically, hydraulic boosters are embodied in such a way that they have a first piston, a second piston, and a booster chamber disposed between the two pistons. One of the two pistons communicates with the piezoelectric actuator, and the boosting depends on the selected ratio between the diameters of the two pistons. Since the first piston, the booster chamber, and the second piston are disposed in line, the known hydraulic booster has a relatively great structural height.
In German Patent Disclosure DE 199 39 452 A1, a hydraulic booster has therefore been proposed in which a first piston is embodied with a cylindrical bore in which the second piston is disposed. The booster chamber is disposed below the first piston, and the second piston is embodied as a stepped piston, so that an annular underside of the second piston is in communication with the booster chamber. Because the second piston is disposed partly in the first piston, the axial structural length of the hydraulic booster is indeed reduced, but because of their special disposition, the two pistons have different directions of motion; that is, the first piston is moved downward by a piezoelectric actuator, while the second piston is moved upward in the first piston. As a result, this booster can be used only for inward-opening valves, since the valve member that is connected to the second piston has the same direction of motion as the second piston.
The valve for controlling fluids of the invention has the advantage over the prior art that it has a hydraulic coupler, in which no reversal of direction of the two pistons occurs; the piston has an especially short length in the axial direction of the valve. In other words, the two pistons of the coupler move in the same direction, making it possible for the coupler to be used in an outward-opening valve. The coupler of the invention can thus be constructed quite compactly and requires only little installation space. Moreover, savings of material can be attained with the coupler of the invention, so that the weight of the coupler in particular is reduced. To that end, the hydraulic coupler of the invention is constructed such that a first piston is embodied as substantially cup-shaped, so that it has both a recess and an inner bottom region. A second piston is disposed in the recess of the first piston, and the coupler chamber, which is filled with a fluid, is disposed between the second piston and the inner bottom region of the first piston. As a result, the hydraulic coupler of the invention can have minimal dimensions in the longitudinal direction of the coupler. It should be noted that a substantially cup-shaped piston is understood to mean a piston that has a bottom region and a wall region encompassing the outer edge of the bottom region. The first piston can for instance have a circular, oval, square, rectangular, or polygonal outer circumference, or some other arbitrary outer circumferential shape. The recess formed by the wall regions of the substantially cup-shaped piston can also have a circular, oval, square, rectangular, or polygonal circumference, or some arbitrary other circumferential shape.
In a preferred version of the present invention, the second piston has a piston face which is the same size as the area of the inner bottom region of the first piston. As a result, it is attained that the hydraulic coupler does not execute any boost in the stroke of the piezoelectric actuator but instead merely compensates for temperature-caused changes in length of the piezoelectric actuator. There is a need for such a hydraulic coupler without a booster function, especially in fuel injection valves with very close tolerances of their structural parts, to avoid magnifying the tolerances.
In another preferred version of the present invention, the piston face of the second piston is smaller in area than the inner bottom region of the first piston. As a result, the hydraulic coupler functions as a booster for boosting the stroke of the piezoelectric actuator. A boost in the actuator stroke is effected as a function of the ratios of the area of the second piston to the area of the inner bottom region of the first piston.
According to the invention, the second piston is guided directly or indirectly in the first piston.
Preferably, a guide element is disposed in the recess of the first piston, for guiding the first piston and the second piston. If the guide element is embodied such that it does not extend as far as the bottom region of the first piston, it is simple to furnish a hydraulic coupler that has a booster function.
Advantageously, the second piston is embodied as a structural unit with a nozzle needle of the valve for controlling fluids. The second piston can either be embodied integrally with the nozzle needle or connected rigidly to the nozzle needle by means of laser welding or screw fastening. In this version, it is possible in particular to dispense with a needle guide for the nozzle needle, since the needle connected rigidly to the second piston is guided by the guide of the piston itself.
In another preferred version of the present invention, the second piston rests directly or indirectly on the nozzle needle. In other words, the second piston and the nozzle needle are not embodied as a structural unit but instead as two separate parts. As a result, it is possible in particular to prevent a recoil, which can occur for instance upon closure of the nozzle needle because of the high pressures and the fast switching times, from being transmitted. Moreover, simple fastening of a needle guide on the nozzle needle is possible.
Preferably, the second piston is likewise embodied as substantially cup-shaped. In particular, the recess of the second piston can be used as a spring seat for a nozzle spring for closing the nozzle needle, if the second piston is embodied as a structural unit with the nozzle needle.
Preferably, a closing spring for the nozzle needle is braced on the second piston. As a result, the number of components can be kept quite low.
Advantageously, a disk or a ring for bracing a restoring spring for the coupler is disposed on the second piston. The restoring spring preferably engages peripheral regions of the first piston, so that after the valve actuation has ended, the coupler can be restored to its outset position.
To make it especially inexpensive and simple to produce, the guide element disposed in the recess of the first piston is preferably embodied as a cylindrical bush. Moreover, the first piston and the second piston preferably also have circular circumferences.
The valve for controlling fluids of the invention is preferably used as a fuel injection valve in common rail or reservoir injection systems, for both Diesel injectors and gasoline injectors.